Joint replacement surgery is a common orthopedic procedure for joints such as the shoulder, hip, knee, ankle and wrist. Prior to implanting prosthetic components in a joint of a patient, a surgeon generally has to resect at least a portion of the patient's native bone in order to create a platform and/or recess or cavity for receiving at least a portion of the prosthetic components being implanted. During the process of resecting bone, a surgeon typically makes an effort to only resect the amount of bone that is needed in order to implant the prosthetic components properly. In other words, it is generally the goal to maintain as much native bone within the joint.
When prosthetic components fail for any one of a variety of reasons, a revision procedure is often necessary. Although defects in a bone adjacent a joint, such as the hip or knee, may occur naturally due to wear and arthritis of the joint and congenital deformities, the removal of a failed prosthetic component also creates an issue with maintaining native bone. Specifically, when prosthetic components are removed from the joint during a revision procedure, it is common for there to have been further native bone loss in the area adjacent the original implant position of the prosthetic components due to movement of the components after implantation or even further degeneration of the bone. For instance, when bone voids are observed in either the proximal tibia or distal femur, or both, after removal of a previously implanted component, it is standard surgical practice to fill those voids as part of the surgical procedure. One way of filling those voids is to use weight bearing void fillers, typically made of an implant-grade metal such as titanium. Such void fillers may be referred to as metaphyseal reconstruction devices (MRD). The name MRD reflects functions such as weight bearing that these devices generally provide.
Because voids in bone are typically irregular in shape, preparation of the bone void area is typically required prior to implantation of a MRD. This preparation (typically by reaming, broaching or milling) ensures there is sufficient room in the bone cavity for the MRD. An accurate fit between the shaped bone cavity and the MRD is important for establishing joint line, and allowing for weight bearing and bone remodeling during the recovery process.
Different methods may be employed to attempt to prepare the bone void area to create an accurate fit between the shaped bone cavity and the MRD. One method is to ream along the intramedullary (IM) axis, followed by broaching. Another method is to ream on the IM axis, followed by freehand burring or bone removal using a rongeur, which may also be followed by broaching. With these methods any reaming performed occurs on the IM axis only, so that void areas at a distance from the IM axis, which commonly occur, can only be resected using manual methods. Also, freehand bone removal, either powered or unpowered, such as by burr or rongeur, often does not produce accurate cavity shapes to receive prosthetic components having predefined configurations. A typical result of the above mentioned methods is that areas remain where the outer walls of the MRD do not contact the cavity, which may lead to undesirable stress distribution and possible loss of bone regrowth. Also typical is the time consuming requirement of iterative bone removal, with multiple checks against the MRD, to obtain a correct fit.
Therefore, there is a need for a surgical instrument that creates accurate bone cavity geometries and minimizes the necessity for freehand bone removal. There is also a need for enabling surgeons to create bone cavities offset from the IM canal with a fully guided system.